Alkenylpyridine synthesis



Nov. 29, 1960 I D. H. WHITE ETAL 2,962,498

ALKENYLPYRIDINE SYNTHESIS Filed Nov. 16, 1953 HEAVY MATERIAL dElW BCIHHDIN V EN TORS.

D. H. WHITE J. M. FOLZ WWW ATTORNEYS United Sm P m O A-LKENYLPYRIDINESYNTHESIS Donald H. White and John M. Folz, Bartlesville, Okla,

assignors to Phillips Petroleum Company, a corporation of Delaware FiledNov. 16, 1953, Ser. No. 392,274

9 Claims. (Cl. 260-290) This invention relates to an improved synthesisprocess for the production of alkenylpyridines by the dehydrogenation ofalkylpyridines. In one of its aspects, it relates to the purificationofalkylpyridines prior to dehydrogenation. In still another of itsaspects, it relates to a safety system as applied'to the purificationsystem.

Alkenylpyridines have received much attention in recent years as asource of monomeric materials for the production of plastics. Althoughalkenylpyridines can be produced commercially by several methods, themethod which is most important commercially is the direct catalyticdehydrogenation of. alkylpyridine tothe corresponding alkenylpyridine.For example, Z-methyl-S-ethylpyridine can be dehydrogenated to producethe corresponding Z-methyl-S-vinylpyridine. Other examples ofalkylpyridines which can be dehydrogenated to form the correspondingalkenylpyridines are 2,4-d-iethylpyridine, 2-ethylpyridine,2,5-d-iethylpyridine, 3ethy1pyridine, 3-propylpyridine,Z-n-amylpyridine, 3-ethyl-4-methylpyridine, 5-isopropyl-Z-methylpyridine, fi-col'lodine and similar compounds. Also,mixtures of alkylpyridines may be dehydrogenarted to give a mixture ofthe corresponding alkenylpyridines.

The alkylpyridines are best prepared by the condensation of a carbonylcompound, that is, an.aldehyde,-ketone or a derivative thereof, withammonia. Examples of carbonyl compounds which can be condensed withammonia to form pyridine derivatives are aldehydes and ketones, i.e.,crotonaldehydes, benzalacetophenone, benzald-iacetophenone, ethylideneacetone, p-chlorobenzaldiaceto phenone, a-acetybutylrolactone,cyclopentanone, tetrahydropyrone, and j8-cyclohexylpropionaldehyde.

Alkenylpyridines can be produced by the condensation of a carbonyl withammonia and the subsequent dehydrogenation of the alkylpyridine.

One difiiculty encountered in the dehydrogenation of alkylpyridines isthe fouling of the dehydrogenation catalyst due to certain impurities,such as polymers, vinylpyridines and picolines, which are produced insmall percentages during the production of the alkylpyridines. Thealkylpyridine can be separated from these impurities by distillation orevaporation, however either some alkylpyridine will be lost with theheavy ends or some heavy ends will be distilled off with thealkylpyridines.

As was hereinbefore stated, the alkylpyridine, as produced, containscertain heavy impurities mixed therein. It is necessary to remove theseimpurities from the alkylpyridine prior to dehydrogenation, since theytend to poison the dehydrogenation catalyst and to foul up the dehydrogenation unit. It is believed that these materials also promotepolymerization of .alkenylpyridines. Most of the alkylpyridine isrecovered by flash evaporation, leaving as a'bottoms product these heavyimpurities along with as much as 50 percent alkylpyridine dissolvedtherein. It is desirable to recover this material for subsequentdehydrogenation.

, 2,962,498 Patented Nov. 29, 1960 erally passes through a heater and isthen flashed into the flash or evaporation zone. Should the flow of newmaterial cease for any cause, the material in the coils of the heaterbecomes charred due to the high temperature of such heater. The cleaningof such tubes is then a difficult and expensive operation.

We have discovered an improved method of preparing alkylpyridines fordehydrogenation and at the same time recovering substantially all of theusable alkylpyridine. We have also discovered a method of preventingdamage to heat exchange tubes in a heater when the flow of materialsthrough said heater should be interrupted.

An object of this invention is to provide a method of purifyingalkylpyn'dines before dehydrogenation and at the same time recoveringsubstantially all of the alkylpyridine. Another object of this inventionis to provide a means of preventing damage to heat exchange tubes in aheat exchange unit when the flow of material through said tubes shouldbe interrupted. Other objects and advantages Will be obvious to thoseskilled in the art upon reading this specification and the attachedclaims.

Our invention comprises heating acrude alkylpyridine from thealkylpyridine production zone in a heating zone and passing the heatedmaterial to a flash zone wherein live steam is added.- The vaporizedalkylpyridine in the flash zone is mixed with superheated steam andpassed into a dehydrogenation zone wherein the alkenylpyridine isformed. The unvaporized fluid from the flash zone, composed of heavymaterials with alkylpyridines dissolved therein, .is passed into a steamstripper wherein the dissolved alkylpyridine is exhaustively strippedalong with some of the heavier polymers. The stripped 2-methyl-S-ethylpyridine (MEP) efiiuent containing some heavy materialisadded'to the diluent from the dehydrogenation zone and the mixturefurther purified. As was indicated hereinbefo're, the heavy ends fromthe flash evaporator contain 50 or more percent heavy materials withalkylpyridine dissolved therein. This material cannot be added directlyto the efiiuent from the dehydrogenation zone since such a largepercentage of heavy material cannot be economically handled in thealkenylpyridine purifying system. The said strippers are used to recovermore than percent of the alkylpyridine from the heavy materials, butinsod'oing, some heavy materials of intermediate boiling range will alsogo off with the alkylpyridine and, for that reason, this material ismixed with the effluent from the dehydrogenation zone. At the same time,we have provided a means of shutting off the heating source to theaforesaid heating zone and atthe same time cooling this'heating zone toa temperature below that which would cause the alkylpyridine to char incase the flowof said alkylpyridine should be interrupted.

Of the many alkenylpyridines known to the art, 2- methyl-S-vinylpyridineis of the most importance commercially at the present time. We willtherefore describe our invention in terms of 2-methyl-5-ethylpyridine(MEP) and the corresponding dehydrogenation product 2-m'ethyl-S-vinylpyridine (MVP).

Our invention can best be desc'ribedby referring to the attached drawingwhich is made a part of thisdisclosure. The drawing is a schematic flowdiagram showing one embodiment of our invention.

Referring to the drawing, crude MEP is removed from MEP storage or feedtank 1 via conduits 2and'3 toh'eating zone 4 wherein the temperature ofthe MEP is raised to a level where some vaporization takes place,usually in the range between 35 0-400 F. The pressure in this zone willusually be inthe range between .10 and 20 p'.s.i. g. In the embodimentshown, the movement of material ,is dependent upon pressuredrop'throughout'the system and, for "that reason, the pressure in'theheating zone will be sive to the temperature of the MEP flowing inconduit 5.

The controller 6 is operatively connected to a valve 7 which controlsthe flow of gas through conduit 8 to burners 9 in heater 4.

It is pointed out that the fluid in conduit can be partially in theliquid state and partially in the vaporous state over a small range oftemperature since the MEP is not pure but contains some heavy oils.crude MEP in conduit 5 can go directly to flash zone 10 via conduit 11or it can pass through soak zone 12 via conduit 13. The soak zone isprovided to allow time for polymerization of vinylpyridines which may bepresent. We have found that substantially all of the 3-vinylpyridinepresent in crude MEP will be sufficiently polymerized by the time thematerial reaches the flash zone 10 without the use of such a soakingzone.

The pressure is dropped to between 5 to 10 pounds per square inch gage(p.s.i.g.) in the flash zone causing most of the MEP to vaporize. Theamount of vaporization is usually between 90 and 97 percent of the totalMEP. The remaining MEP is dissolved in the heavy material which settlesin the bottom of the said flash zone.

A small amount of steam is admitted to the bottom of the flash zone viaconduit 14. This steam is used to strip the heavy material which goes tobatch strippers 15 or 16 via conduits 17 and 18. These batch strippersare so arranged that one stripper can be fed while the material in theother stripper is being exhaustively stripped and the stripped heavymaterial is being dumped.

The heavy material will contain between 50 and 75 percent MEP as itenters the stripper and the total flow will amount to approximately 5percent of the material entering the flash zone. Steam is admitted tothe bottom of the said stripper via steam conduits 45. The steam isadmitted during the time the heavy material is flowing to said stripperand the stripping started. When the The hot 7 level of crude heavymaterial has reached the desired level in the stripper, the flow of saidmaterial will be switched to the other stripper and the material in thefirst stripper will be further stripped until less than 5 percent MEPremains in the heavy material. The efiiuent from said stripper isremoved through conduit 46. When the heavy material has been stripped to5 percent or less MEP, the steam is cut off and the stripped heavymaterial is dumped through conduits 19. The stripper is then ready foranother charge of heavy materials. This final stripping and dumping ofthe stripper takes place while the second stripper is being filled.During the final stripping in one stripper and the filling of the otherstripper, the etliuents from both strippers are taken off via conduit46.

The vaporized MEP is removed from the flash zone 10 via conduit 20.Superheated steam at 1206-1500 F. is admitted to conduit 20 via steamconduit 21 and the resulting mixture is passed over a dehydrogenationcatalyst in dehydrogenation zone 22 where the MEP is dehydrogenated toMVP. Some picolines, heavy oils and unreacted MEP will also be presentin the resulting MVP. This crude MVP is removed via conduit 25 to wasteheat boiler 24. The crude MVP is cooled in the waste heat boiler 24 bygiving up some of its heat to water passing through said waste heatboiler, this water being vaporized to pound steam. The crude MVP is notcooled sutiiciently to cause condensation. The crude MVP is removed fromthe waste heat boiler via conduit 25 and is mixed with the efiiuent fromthe aforesaid strippers 15 or 16 in conduit 18 and is passed tofractionator 37. MEP efiluent from the said fractionator is returned toMEP feed tank 1 via conduit 38. MVP

4 and heavy material is sent via conduit 39 to still 40 where the MVP isdistilled off through conduit 41. The heavy bottoms from still 40 isremoved via conduit 42. The 30 pound steam system, as shown, is atypical waste heat recovery system and needs no further discussion.

The flow of crude MEP feed from feed tank 1 to heater 4 passes throughflow detector 27. Air valve 28 is electrically operatively connected viaelectrical conduit 43 with flow detector 27 so that valve 28 will open,admitting air pressure to conduit 34 which in turn opens normally closedvalve 35, admitting air to conduits 29 and 30 when the flow of materialthrough the detector decreases below a predetermined rate. Valve 35contains a small bleed hole 36 which prevents air leakage through valve28 causing the system to be activated. The air pressure in conduit 29closes gas valve 31, thereby interrupting the flow of gas to burners 9.The air pres sure in conduit 30 opens steam valve 32 admitting steam tothe heater 9 via conduit 33 and thereby cooling said heater.

Our invention has been described in one of its preferred embodiments.Those skilled in the art will see many changes which can be made withoutdeparting from the scope of our invention. For example, the low pressuresteam generating system can be eliminated. The steam from such a systemcan be used for supplying steam to conduits 14, 17 and 33. The pressuresand temperatures are not limited to those disclosed, but any pressureand temperature as is known in the art can be employed. There can beseveral batch strippers instead of the two as shown or a singlecontinuous type stripper can be used.

We claim:

1. A process for purification and dehydrogenation of alkylpyridines, thesaid process comprising heating crude alkylpyridine under pressure,reducing the said pressure and thereby evaporating only a portion but atleast percent of the alkylpyridine from the crude feed, dehydrogenatingthe evaporated alkylpyridine, steam stripping the unevaporated material,mixing the resulting alkylpyridine-rich eflluent from said steamstripping with the dehydrogenated pyridine, fractionating the resultingmixture into an alkylpyridine rich fraction and an alkenylpyridine richfraction and recycling the alkylpyridine rich fraction to said heatingstep.

2. A process for the purification and dehydrogenation of crudealkylpyridines consisting of alkylpyridines and higher boilingmaterials, the said process comprising the steps of heating the crudealkylpyridine, vaporizing only a portion but at least 90 percent of thealkylpyridine from the crude material, adding superheated steam to thevaporized alkylpyridine, passing the resulting mixture through adehydrogenation zone thereby producing a crude alkenylpyridine, passingthe unvaporized crude alkylpyridine to a stripping zone, steam strippingunvaporized alkylpyridine along with some heavier ma terial from saidunvaporized crude alkylpyridine; mixing the alkylpyridine-rich efiiuentfrom said steam stripping with the crude alkenylpyridine, fractionatingthe resulting mixture into an alkylpyridine rich fraction and analkenylpyridine rich fraction, recovering the alkenylpyridine richfraction and recycling the all ylpyridine rich fraction to said heatingstep.

3. A process for the purification and dehydrogenation of crudealkylpyridine consisting of alkylpyridine and higher boiling components,the said process comprising heating the crude alkylpyridine to atemperature in the range of 350 to 400 F. under a pressure in the rangeof 10 to 20 p.s.i.g., reducing the pressure to 5 to 10 p.s.i. g. therebycausing most of the alkylpyridine to vaporize, mixing steam in thetemperature range of 1200 to l500 F. with the vaporized alkylpyridine,passing the resulting mixture over a dehydrogenation catalyst therebyproducing a crude alkenylpyridine, said crude alkenylpyridine comprisingalkenylpyridine, unreacted alkylpyridine,

and picolines; stripping the remaining alkylpyridine along with someheavier material from the unvaporized crude alkylpyridine, mixing thealkylpyridine-rich eifluent from said stripping with the crudealkenylpyridine, fractionating the resulting mixture into analkylpyridine rich fraction and an alkenylpyridine rich fraction;recovering alkenylpyridine from said alkenylpyridine rich fraction andrecycling the alkylpyridine rich fraction to the first heating step.

4,. The process of claim 3 wherein the alkylpyridine is2-methyl-5-ethylpyridine and the alkenylpyridine is 2-methyl-S-vinylpyridine.

5. The process of claim 3 wherein the alkylpyridine is 3-ethylpyridineand wherein the alkenylpyridine is 3- vinylpyridine.

6. The process of claim 3 wherein the alkylpyridine is3-ethyl-4-methylpyridine and wherein the alkenylpyridine is3-vinyl-4-methylpyridine.

7. The process of claim 3 wherein the alkylpyridine isS-isopropyl-Z-methylpyridine and wherein the alkenylpyridine is5-isopropenyl-2-methyl-pyridine.

8. The process of claim 3 wherein the alkylpyridine is mixedalkylpyridines and wherein the alkenylpyridine is mixedalkenylpyridines.

9. In the process for preparing crude alkylpyridine for dehydrogenation,said crude alkylpyridine comprising alkylpyridine and higher boilingmaterial, the steps comprising passing hot crude alkylpyridine through avaporizing zone wherein only a portion of the alkylpyri dine isvaporized; passing the vaporized alkylpyridine to a dehydrogenationzone; passing the unvaporized material from the said vaporizing zone toa stripping zone with steam; steam stripping the remaining alkylpyridinefrom the unvaporized material, mixing the alkylpyridine-rich efiluentfrom the said stripping zone with the product from the dehydrogenationzone, recovering the unreacted alkylpyridine from the resulting mixture,and returning the unreacted material to the purification system.

References Cited in the file of this patent UNITED STATES PATENTS1,895,086 Porter Jan. 24, 1933 2,389,793 Livingston Nov. 27, 19452,514,207 Johnson July 4, 1950 2,606,103 Hamm Aug. 5, 1952 2,611,769Hays Sept. 23, 1952 2,677,688 Burrows et al. May 4, 1954 2,697,067Reynolds Dec. 14, 1954 2,745,833 Stoops et al May 15, 1956 FOREIGNPATENTS 488,593 Canada Dec. 2, 1952 OTHER REFERENCES Perry: Chem. Eng.Handbook (McGraw-Hill, 3rd ed.), p. 585 (1950).

1. A PROCESS FOR PURIFICATION AND DEHYDROGENATION OF ALKKYLPYRIDINES,THE SAID PROCESS COMPRISING HEATING CRUDE ALKYLPYRIDINE UNDER PRESSURE,REDUCING THE SAID PRESSURE AND THEREBY EVAPORATING ONLY A PORTION BUT ATLEAST 90 PERCENT OF THE ALKYLPYRIDINE FROM THE CRUDE FEED,DEHYDROGENATING THE EVAPORATED ALKYLPYRIDINE, STEAM STRIPING THEEVAPORATED MATERIAL, MIXING THE RESULTING ALKYLPYRIDINE-RICH EFFLUENTFROM SAID STEAM STRIPPING WITH THE DEHYDROGENATED PYRIDINE,FRACTIONATING THE RESULTING MIXTURE INTO AN ALKYPYRIDINE RICH FRACTIONAND AN ALKENYL PYRIDINE RICH FRACTION AND RECYCLING THE ALKYLPYRIDINERICH FRACTION TO SAID HEATING STEP.